Umbraco-CMS/src/Umbraco.Web/PublishedPropertyExtension.cs

using System.Collections.Generic;
using Umbraco.Core;
using Umbraco.Core.Composing;
using Umbraco.Core.Models.PublishedContent;

namespace Umbraco.Web
{
    /// <summary>
    /// Provides extension methods for <c>IPublishedProperty</c>.
    /// </summary>
    public static class PublishedPropertyExtension
    {
        // see notes in PublishedElementExtensions
        //
        private static IPublishedValueFallback PublishedValueFallback => Current.PublishedValueFallback;

        #region Value

        public static object Value(this IPublishedProperty property, string culture = null, string segment = null, Fallback fallback = default, object defaultValue = default)
        {
            if (property.HasValue(culture, segment))
                return property.GetValue(culture, segment);

            return PublishedValueFallback.TryGetValue(property, culture, segment, fallback, defaultValue, out var value)
                ? value
                : property.GetValue(culture, segment); // give converter a chance to return it's own vision of "no value"
        }

        #endregion

        #region Value<T>

        public static T Value<T>(this IPublishedProperty property, string culture = null, string segment = null, Fallback fallback = default, T defaultValue = default)
        {
            if (property.HasValue(culture, segment))
            {
                // we have a value
                // try to cast or convert it
                var value = property.GetValue(culture, segment);
                if (value is T valueAsT)
                {
                    return valueAsT;
                }

                var valueConverted = value.TryConvertTo<T>();
                if (valueConverted)
                {
                    return valueConverted.Result;
                }

                // cannot cast nor convert the value, nothing we can return but 'default'
                // note: we don't want to fallback in that case - would make little sense
                return default;
            }

            // we don't have a value, try fallback
            if (PublishedValueFallback.TryGetValue(property, culture, segment, fallback, defaultValue, out var fallbackValue))
            {
                return fallbackValue;
            }

            // we don't have a value - neither direct nor fallback
            // give a chance to the converter to return something (eg empty enumerable)
            var noValue = property.GetValue(culture, segment);
            if (noValue is T noValueAsT)
            {
                return noValueAsT;
            }

            var noValueConverted = noValue.TryConvertTo<T>();
            if (noValueConverted)
            {
                return noValueConverted.Result;
            }

            // cannot cast noValue nor convert it, nothing we can return but 'default'
            return default;
        }

        #endregion
    }
}